How to write an invoice (with everything it legally needs)

An invoice is just a clear request for money. Most small businesses overthink it, then leave off the one thing the client's accounts team needs to pay it. Here's the whole checklist.

The 9 things every invoice needs

The word "Invoice" — obvious, but bookkeeping software and inboxes filter on it.
A unique invoice number — sequential (INV-0041, INV-0042…). Never reuse one; it's how both sides refer to it later.
Your business details — legal name, address, email, phone. If you're registered for GST or VAT, your tax number must be on it.
The client's details — business name and address. For companies, add the contact person so it lands with the right human.
The issue date — the day you send it.
The due date — a real date ("Due 1 October 2026"), not "net 14". People pay dates, not maths.
What you did — one line per item or service, with quantity and unit price. Be specific enough that someone who wasn't there understands it.
The totals — subtotal, tax (with the rate), and the total due. If a deposit was paid, show it and the balance.
How to pay — bank account, or a pay-online link. Add "please use INV-0042 as the reference" so the payment is easy to match.

What's optional but worth including

A PO number, if the client gave you one. Large companies won't pay without it.
Payment terms, one line: "Payment due within 14 days. 2% late fee after 7 days overdue."
A short thank-you. It's free and it makes the next email easier.

Tax on invoices: the short version

If you're registered for GST (NZ, Australia), VAT (UK, EU), or sales tax (US states), the invoice must show your registration number, the tax rate, and the tax amount separately from the subtotal. In New Zealand a tax invoice over $1,000 must also include the words "Tax Invoice" — most tools add this automatically. Not registered? Leave tax off entirely and say so if clients ask.

The details that get you paid faster

Send it the same day you finish the job. Every day of delay is a day the client spends the money elsewhere.
Email it to the person who pays, not the person who hired you. Ask "who should invoices go to?" when you start.
Offer a way to pay in one tap. Invoices with a Pay now button get paid roughly twice as fast as bank-transfer-only invoices.
Set a due date 7–14 days out. Thirty-day terms are a habit from big companies; small clients pay small invoices quickly if you ask.
Let reminders do the chasing. A polite automatic reminder on the due date and a firmer one a week later removes the awkwardness.

Free template vs. an invoicing tool

A Word or Excel template works for your first few invoices. Once you have repeat clients, numbering, tracking who has paid, and chasing become the real work — and that's where a tool pays for itself. You can create a proper invoice for free with our invoice generator, and if you want numbering, reminders and online payment, your first 10 invoices are free.